1. Field of the Invention
The invention relates to a fuel filter with a filter element for filtering out particles and water from a fuel flowing through the fuel filler, and a water drainage unit for removing the filtered-out water from the filter.
2. Description of the Prior Art
In motor vehicles that are driven by a diesel engine, for example, fuel filters of the type mentioned above are used to filter out particles and water contained in the diesel fuel. The fuel is filtered to prevent malfunctions or damage such as corrosion from occurring, particularly in an injection system of the associated engine. Such damage can be caused by water residue in the fuel.
For the above-mentioned reason, a maximum permissible percentage of water in diesel fuel of less than 200 mg/l is codified in DIN EN 590. In order to achieve such a limit value, conventional fuel filters are equipped with a filter element that holds back particles and separates out water from the flowing fuel. The separated water travels into a water drainage unit, which is impassible to the actual fuel. In the water drainage unit, underneath the filter element, a sump is often provided, in which the water separated out from the fuel can collect. The water that collects in the sump must be emptied regularly, for which purpose special outlet- or valve elements must be provided.
DE 101 38 695 A1 has disclosed a device for drawing water from the fuel system of an internal combustion engine in which the separated water is collected in a sump until a water sensor detects a minimum level of water. Then a shut-off device is opened through which the water can be discharged or conveyed to a second water drainage unit. A disadvantage of this embodiment is that if the water sensor malfunctions, then the water is never emptied from the water drainage unit of the fuel filter. Aside from this susceptibility to malfunction, this embodiment is also comparatively expensive since it requires a water sensor, a shut-off device, and associated control electronics.
JP 61-216701 has also disclosed a fuel filter in which a water drainage unit is situated underneath a filter element. The membrane of the water drainage unit is clamped between two housing parts of the fuel filter so as to achieve a closed structural unit. As a result, the water drainage unit is situated on the clean side of the filter element.
JP 64-11609 has disclosed an automatic water separation device for a fuel supply system in which a water drainage unit situated underneath a filter element is embodied with a first hydrophilic membrane and a hydrophobic membrane situated downstream of it in the flow direction of the separated water.